Hearts may be warm Sunday for Valentine's Day, but the weather across the eastern U.S. is ice cold.

Freezing temperatures and strong winds in such major cities as Boston, New York, Baltimore and Washington are making it dangerous to spend long periods outdoors, with the thermometer reading as low as minus 37 degrees Celsius in some places.

"It's so important to take this seriously, to stay indoors to the maximum extent possible," New York Mayor Bill de Blasio warned Saturday.

It was cold enough Saturday in New York to cancel the annual Central Park Ice Festival. Trucks in New York and elsewhere have been picking up homeless men and women and taking them to shelters and hospitals.

A strong snow shower is blamed for an accident Saturday on a Pennsylvania highway near Philadelphia that left about 50 cars in a twisted pile. Several deaths are reported.

Forecasters say the bitterly cold weather will last through Monday, when snow will change to rain as temperatures warm up to the high single digits Celsius overnight into Tuesday.